Microsoft today confirmed it has been pre-loading the Windows 10 installation bits onto devices whose owners have not “reserved” a copy or expressed interest in the new OS.

The move has upset some users of Windows 7 and Windows 8.1, who have complained that the unsolicited downloads have caused them to exceed their Internet providers’ data caps or seized storage space without their consent.

“For those who have chosen to receive automatic updates through Windows Update, we help customers prepare their devices for Windows 10 by downloading the files necessary for future installation,” a company spokeswoman said in an email. “This results in a better upgrade experience and ensures the customer’s device has the latest software. This is an industry practice that reduces time for installation and ensures device readiness.”

If Windows 7 or Windows 8.1 device owners have Windows Update set to the default — and Microsoft-recommended — option that lets the operating system download and install security and other bug fixes automatically in the background, Microsoft will push the Windows 10 upgrade files to the drive.

The upgrade, which can range in size from more than 3GB to nearly 6GB, is placed in the hidden “$Windows.~BT” folder, a long-used destination for Windows upgrades. It will sit there, presumably until the user expresses some kind of desire to install Windows 10.

After the Windows 10 upgrade was downloaded to the device, the user was notified through the app that it was ready to install.

This new scheme, however, is vastly different in that the bits are downloaded to the device even though the user has not asked for the upgrade.

Not surprisingly, among the first to notice the I-did-not-ask-for-this upgrade were people who have data caps mandated by their Internet service providers (ISPs), particularly those who relied on a cellular connection to the Internet.

Several commenters in a long thread on Slashdot claimed that they had exceeded their caps because Microsoft downloaded the massive upgrade to their hardware without their approval.

“I had to travel recently, so I took a laptop with [a] clean Windows 8.1 Pro install,” wrote one such user, identified only as “X.25″ on Slashdot. “At my destination, I purchased a SIM (they only had 1GB data packages) and put it into the 3G/W-Fi router I carry. I powered the laptop, connected to [the] Internet via said router, checked [a] few things, then went away for [a] few hours. When I got back to [the] apartment, my data package (and Internet connectivity) was killed because [the] Microsoft idiots decided to start downloading Windows 10 even though I have explicitly closed/rejected all the ‘offers.'”

Others didn’t appreciate the unwelcome guest that dropped into their limited storage space. Anyone with a 128GB SSD (solid-state drive), for example, would be concerned if 5% of their storage capacity was occupied without their okay.

Some also wondered whether Microsoft would take the next logical step by either dunning users with notifications urging them to apply the already-installed upgrade, or make the much more unlikely move of automatically triggering the upgrade.

The former would, frankly, not be that different from what Microsoft has already done with those who accepted the free upgrade and reserved a copy. It’s possible that many on the receiving end of such notifications would approve the upgrade, and even appreciate the fact that they did not have to wait for a long download to complete before upgrading. The latter, however, would be unprecedented, and would almost certainly fuel a firestorm of protest.

Microsoft did not immediately reply to follow-up questions about its intensions.

What is also interesting about the upgrade-prep is Microsoft’s defense, that it’s an “industry practice.”

Although that may be true in limited instances — Google’s Chrome browser, for example, regularly pre-loads updates, which are then automatically installed the next time the application is launched — as far as Computerworld knows, it’s never been done with either an operating system or software that demands installation files of this size. The most common practice for operating systems, by far, is to begin downloading an upgrade only after the user has been notified, and then approved the procedure.

Wes Miller, an analyst with Directions on Microsoft, agreed. “I’ve seen some tiny apps do it for updates. But not for an OS upgrade,” Miller said in an email answer to a question asking whether he recalled any similar examples.